1. Field of the Invention
The present invention relates to a photoconductor for electrophotography, and more particularly to a photoconductor for electrophotography which includes an electroconductive substrate having thereon a photosensitive layer containing a diamine compound.
2. Description of the Prior Art
Photosensitive materials conventionally used in photoconductors for electrophotography (hereafter, sometimes referred to simply as "photoconductors") include inorganic photoconductive substances such as selenium or selenium alloys, photoconductive materials containing inorganic photoconductive substances such as zinc oxide or cadmium sulfide dispersed in a binder resin, organic photoconductive substances such as poly-N-vinylcarbazole, or polyvinylanthracene, and organic photoconductive materials containing organic photoconductive substances such as phthalocyanin compounds or bisazo compounds dispersed in a binder resin or vacuum deposited on a suitable substrate. Photoconductors must have a function of maintaining surface charges in the dark, a function of generating charges upon receipt of light, and a function of transporting the generated charges upon receipt of light. There are two types of photoconductors, i.e., a monolayer type photoconductor which has all the above-mentioned functions in a single layer, and a laminated type one in which the above-mentioned functions are shared by a charge generating layer contributing mainly to generation of charges and a charge transporting layer contributing mainly to maintaining charges in the dark and transportation of charges upon receipt of light.
The electrophotographic image formation using these photoconductors is made, for example, according to the Carlson's method, in which a photoconductor is subjected in the dark to corona discharge to charge the photoconductor, the surface of the charged photoconductor is imagewise exposed to light using a manuscript or copy bearing, e.g., letters and/or pictures to form a latent electrostatic image, the thus formed latent electrostatic image is developed with a toner to form a visible image, the developed toner image is transferred to a support such as a paper sheet to fix the toner image on the support. After the toner image transfer, the photoconductor is subjected to the steps of removal of the electric charge and removal of the remaining toner (cleaning), and the like to be ready for reuse for a prolonged period of time.
Photoconductors for electrophotography utilizing organic materials have recently been studied and put into use because of their advantageous features such as flexibility, thermal stability, film-forming properties, and so on. Various charge transporting substances are known from, for example, U.S. Pat. No. 3,189,447 which discloses oxadiazole compounds, Japanese Patent Publication No. 2023/1984 pyrazoline compounds, Japanese Patent laying-open Nos. 42380/1980, 101844/1982, and 150128/1979 hydrazone compounds, respectively, as charge transporting substances.
Incidentally, many of the photoconductors currently put into practical use are of function-separated type and include a charge generating layer and a charge transporting layer. For example, Japanese Patent Publication No. 42380/1980 discloses a function-separated type photoconductor which uses chlorocyan blue as a charge generating substance and a hydrazone compound as a charge transporting substance. It is expected that this results in a photoconductor having a high sensitivity and a high durability. While organic materials have many advantages that inorganic materials do not have, there has been obtained no organic material that meets all the characteristics required for photoconductors for electrophotography. In particular, low durability is now at stake.
The decrease in durability is considered to be ascribable to decrease in sensitivity, increase in residual potential, decrease in chargeability, blurring of image, occurrence of white spots, or black spots, after prolonged use, as well as increase in residual potential, decrease in chargeability and mechanical wear of the surface of the photoconductor under the conditions of high temperature and high humidity, or low temperature and low humidity, and so on.
Deterioration of electric characteristics is considered to be ascribable to chemical deterioration of the charge transporting substance contained in the surface layer of the photoconductor, i.e., oxidation or photolysis with ozone, NO.sub.x or the like formed concomitantly with corona discharge. It is considered that physicochemical factors are also involved in the deterioration of electric characteristics. For example, crystallization and deposition of the charge transporting substance in the charge transporting layer, morphological change of the charge transporting substance between the interface of the charge generating, layer and the charge transporting layer.
Various trials have been made in order to increase the durability of photoconductors. For example, it has been proposed to add an ultraviolet absorbent or antioxidant in the photosensitive layer of the photoconductor, to develop binder resins having improved compatibilities with the charge transporting substance. However, further improvement is desired.